umask: Correctly handle empty symbolic value

Simple return/echo confusion.

Fixes #10177

share/functions/umask.fish

@@ -39,7 +39,8 @@ set __fish_umask_set_table 6 5 4 3 2 1 0
 function __fish_umask_set
     set -l to_set $argv[1]
     if test $to_set -eq 0
-        return 7
+        echo 7
+        return
     end
     echo $__fish_umask_set_table[$to_set]
 end

tests/checks/umask.fish

@@ -89,3 +89,10 @@ umask
 umask -S
 #CHECK: 0222
 #CHECK: u=rx,g=rx,o=rx
+
+umask u=rwx,g=rwx,o=
+umask
+#CHECK: 0007
+umask u=rwx,g=,o=rwx
+umask
+#CHECK: 0070